Cinema, as Jean-Luc Godard wrote, is truth 24 times a second. Documentaries both prove and disprove the point; but the truth is their strongest weapon. Here, Guardian and Observer critics pick the 10 best

Continuing our 10-part, alphabetically organised list of important titles of 2013, feast your antennae on new films from The Guard's John Michael McDonagh and Ridley Scott, as well as a Princess Diana biopic and a departure for Errol Morris

Standard Operating Procedure by Philip Gourevitch and Errol Morris examines the official policy of torture in Abu Ghraib prison and those men and women who were ordered to carry it out, says Rafael Behr

Errol Morris expected to hate the man who sent the US into Vietnam. But when he started filming The Fog of War, his documentary about Robert McNamara, something extraordinary happened: they got along. Desson Thomson hears both stories.